Detailed investigations continue on the molecular basis of calcium and phosphate absorption system, and the effect of vitamin D and other factors and conditions on these processes. These include: (a) finalization of the amino acid sequence of the bovine vit. D-dependent calcium-binding protein and continued studies on its Ca-binding properties and structural modifications by Ca ion 2, (b) initiation of the sequence of the chick vitamin D-dependent calcium-binding protein, (c) isolation, characterization and localization of a vitamin D-responsive microvillar glycoprotein, (d) isolation and characterization of a temperature-sensitive calcium-binding protein from pig ileum, (e) isolation of basal-lateral membranes with the purpose of characterizing the "Ca-pump", localized on these membranes, (f) continued studies on the phosphate transport system, using isolated chick intestinal cells.